Wet-laid microfibers including polyolefin and thermoplastic starch

ABSTRACT

Spun microfibers include a blend of 70 wt. % to 90 wt. % meltblown-grade polyolefin and 10 wt. % to 30 wt. % thermoplastic starch, wherein the microfibers are suitable for use in a wet-laid process. A method for producing an absorbent product includes producing a blend of 70 wt. %-90 wt. % meltblown-grade polyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch (TPMS), wherein the blend prior to spinning has a melt flow index greater than 150; spinning the blend into microfibers in a fiber spinning process; cutting the microfibers into staple fibers; and incorporating the staple fibers into a wet-laid process for making a nonwoven web.

BACKGROUND

Current wet-laid microfibers are produced with a limited number offiber-grade synthetic polymers such as PE, PP, PET, and PLA. The limitednumber of options for fiber-grade polymers is due to a set of stringentrequirements for fiber melt spinning. There are no wet-laid microfiberscontaining biopolymers such as starch, although thermoplastic starch iswidely used in blends of polyolefin or PLA for breathable, stretchable,or packaging film applications.

In an attempt to increase sustainability, thermoplastic modified starch(TPMS) can be added to fiber-grade polyolefins. The resulting fibers,however, such as those in U.S. Pat. No. 6,623,854 to Bond, cannot bespun without the fibers breaking, except at very low speeds, which isinefficient, costly, and inappropriate for commercial production. UsingTPMS with standard fiber spinning grades of polyolefins does not allowcommercial scale speeds. Further, TPMS and meltblown-grade polyolefinscannot be spun into fiber individually using staple fiber spinningequipment because their melt-flow indexes (MFIs) are insufficient. TPMShas an MFI that is too low, whereas meltblown-grade polyolefins have anMFI that is too high.

U.S. Pat. No. 8,470,222 B2 to Shi et al. describes a biodegradable fiberspun from blends of modified aliphatic-aromatic polyester and TPMS. Thereason to modify aliphatic-aromatic polyester via alcoholysis is becausethermoplastic starch alone cannot be spun into fibers due to itsunfavorable rheological characteristics. The modified aliphatic-aromaticpolyester can alter rheological profile of thermoplastic starch suitablefor fiber melt spinning. However, polyester resins are expensiverelative to polyolefins and alcoholysis through reactive extrusion caninvolve the use of undesirable chemical reagents. The disclosuredescribed herein directly blends meltblown-grade polyolefins andthermoplastic modified starch for wet-laid microfiber spinning. Theresults demonstrate an unexpected success to spin fibers from blends ofmeltblown-grade polyolefin and thermoplastic starch. Conversely, asdescribed above, conventional fiber-grade polyolefin containing TPMScannot be realistically spun into fibers.

It is well known that few renewable materials by themselves are suitablefor fiber spinning. Attempts to date have dealt with improvingprocessability for renewable materials such as starch in theirrespective blends for fiber spinning. Different processing aids wereadded into fiber blends. However, there is no direct use of meltblownsynthetic polymers in their blends.

SUMMARY

The present disclosure describes novel fiber compositions usingmeltblown polyolefins and thermoplastic modified starch to createmiscible blends for wet-laid microfiber spinning via conventionalpolymer processing equipment.

This disclosure addresses the use of a low-cost starch biopolymertogether with a commodity meltblown-grade polyolefin for wet-laidmicrofiber production. Successful inclusion of thermoplastic starch inmeltblown-grade polyethylene or polypropylene for wet-laid microfiberspinning creates opportunities in 1) cost reduction when it is used inbath/facial tissue or towel manufacturing, and in 2) increased use ofbio-based renewable material content, all of which is consistent withsustainability objectives.

More specifically, synthetic microfibers are made in a conventionalfiber spinning process (not a meltblown process) from a blend ofmeltblown-grade polyolefin(s) and thermoplastic modified starch (TPMS).These blends can be made with or without a compatibilizer, such asmaleic anhydride grafted polymers or polar-group grafted polymericadditives or coupling agents. The wet-laid microfiber can be in anycross-sectional configurations such as monofilament, side-by side,island-in-the sea, or sheath-core structures. The fibers can be cut intostaple fibers or used as a continuous fiber without cutting. For tissueapplications, the fibers are cut into lengths less than 5 mm, with anormal range of 1 to 3 mm long.

In one aspect, spun microfibers include a blend of 70 wt. % to 90 wt. %meltblown-grade polyolefin and 10 wt. % to 30 wt. % thermoplasticstarch, wherein the microfibers are suitable for use in a wet-laidprocess.

In another aspect, a method for producing spun microfibers includesproducing a blend of 70 wt. %-90 wt. % meltblown-grade polyolefin with10 wt. % to 30 wt. % thermoplastic modified starch (TPMS) derived fromnative starch; and spinning the blend into microfibers in a fiberspinning process, wherein the microfibers are suitable for use in awet-laid process.

In still another aspect, a method for producing an absorbent productincludes producing a blend of 70 wt. %-90 wt. % meltblown-gradepolyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch(TPMS), wherein the blend prior to spinning has a melt flow indexgreater than 150; spinning the blend into microfibers in a fiberspinning process; cutting the microfibers into staple fibers; andincorporating the staple fibers into a wet-laid process for making anonwoven web.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features and aspects of the present disclosureand the manner of attaining them will become more apparent, and thedisclosure itself will be better understood by reference to thefollowing description, appended claims and accompanying drawings, where:

FIG. 1 graphically illustrates Differential Scanning calorimeter (DSC)thermograms (2nd heat) of PP/TPMS blend samples;

FIG. 2 graphically illustrates the effect of composition (Wt % TPMS) onmelt temperature of PP/TPMS blends; and

FIG. 3 graphically illustrates the effect of composition (Wt % TPMS) onmelt enthalpy of PP/TPMS blends.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present disclosure. The drawings are representationaland are not necessarily drawn to scale. Certain proportions thereofmight be exaggerated, while others might be minimized.

DETAILED DESCRIPTION

The terms “absorbent article” and “absorbent product” refer herein to anarticle that can be placed against or in proximity to the body (i.e.,contiguous with the body) of the wearer to absorb and contain variousliquid, solid, and semi-solid exudates discharged from the body. Suchabsorbent articles, as described herein, are intended to be discardedafter a limited period of use instead of being laundered or otherwiserestored for reuse. It is to be understood that the present disclosureis applicable to various disposable absorbent articles, including, butnot limited to, diapers, training pants, youth pants, swim pants,feminine hygiene products, including, but not limited to, menstrualpads, incontinence products, medical garments, surgical pads andbandages, other personal care or health care garments, and the likewithout departing from the scope of the present disclosure. The term canalso include bath tissue, facial tissue, toweling, and the like.

The term “carded web” refers herein to a web containing natural orsynthetic staple fibers typically having fiber lengths less than about100 mm. Bales of staple fibers can undergo an opening process toseparate the fibers that are then sent to a carding process thatseparates and combs the fibers to align them in the machine directionafter which the fibers are deposited onto a moving wire for furtherprocessing. Such webs are usually subjected to some type of bondingprocess such as thermal bonding using heat and/or pressure. In additionto or in lieu thereof, the fibers can be subject to adhesive processesto bind the fibers together such as by the use of powder adhesives. Thecarded web can be subjected to fluid entangling, such ashydroentangling, to further intertwine the fibers and thereby improvethe integrity of the carded web. Carded webs, due to the fiber alignmentin the machine direction, once bonded, will typically have more machinedirection strength than cross machine direction strength.

The term “hydrophilic” refers herein to fibers or the surfaces of fibersthat are wetted by aqueous liquids in contact with the fibers. Thedegree of wetting of the materials can, in turn, be described in termsof the contact angles and the surface tensions of the liquids andmaterials involved. Equipment and techniques suitable for measuring thewettability of particular fiber materials or blends of fiber materialscan be provided by Cahn SFA-222 Surface Force Analyzer System, or asubstantially equivalent system. When measured with this system, fibershaving contact angles less than 90 degrees are designated “wettable” orhydrophilic, and fibers having contact angles greater than 90 degreesare designated “nonwettable” or hydrophobic.

The term “meltblown” refers herein to fibers formed by extruding amolten thermoplastic material through a plurality of fine, usuallycircular, die capillaries as molten threads or filaments into converginghigh velocity heated gas (e.g., air) streams that attenuate thefilaments of molten thermoplastic material to reduce their diameter,which can be a microfiber diameter. Thereafter, the meltblown fibers arecarried by the high velocity gas stream and are deposited on acollecting surface to form a web of randomly dispersed meltblown fibers.Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 toButin et al., which is incorporated herein by reference. Meltblownfibers are microfibers that can be continuous or discontinuous, aregenerally smaller than about 0.6 denier, and can be tacky andself-bonding when deposited onto a collecting surface.

The term “nonwoven” refers herein to materials and webs of material thatare formed without the aid of a textile weaving or knitting process. Thematerials and webs of materials can have a structure of individualfibers, filaments, or threads (collectively referred to as “fibers”)that can be interlaid, but not in an identifiable manner as in a knittedfabric. Nonwoven materials or webs can be formed from many processessuch as, but not limited to, meltblowing processes, spunbondingprocesses, carded web processes, etc.

The term “pliable” refers herein to materials that are compliant andthat will readily conform to the general shape and contours of thewearer's body.

The term “spunbond” refers herein to small diameter fibers that areformed by extruding molten thermoplastic material as filaments from aplurality of fine capillaries of a spinnerette having a circular orother configuration, with the diameter of the extruded filaments thenbeing rapidly reduced by a conventional process such as, for example,eductive drawing, and processes that described in U.S. Pat. No.4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner et al.,U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No.3,502,538 to Peterson, and U.S. Pat. No. 3,542,615 to Dobo et al., eachof which is incorporated herein in its entirety by reference. Spunbondfibers are generally continuous and often have average deniers largerthan about 0.3, and in an aspect, between about 0.6, 5 and 10 and about15, 20 and 40. Spunbond fibers are generally not tacky when they aredeposited on a collecting surface.

The term “thermoplastic” refers herein to a polymeric material thatbecomes pliable or moldable above a specific temperature and returns toa solid state upon cooling.

The term “meltblown-grade polyolefin” refers to a polyolefincharacterized by an extremely high melt flow rate homopolymer resin. Themelt flow rate of a meltblown-grade polyolefin can range from 200 to1550 g/10 min under standard testing conditions (ISO 1133-1).Meltblown-grade polyolefins can also have a narrow molecular weightdistribution.

The term “microfiber” refers to a fiber (including staple fibers andfilaments) with a linear mass density less than 1 dtex, where dtex is anabbreviation of decitex, the mass in grams per 10,000 meters.

Generally, a method of producing wet-laid microfibers using spunbondTPMS and meltblown-grade polymers is disclosed herein. This disclosureaddresses the use of a low-cost starch biopolymer together with alow-cost commodity meltblown-grade polyolefin for wet-laid microfiberproduction. Successful inclusion of thermoplastic starch inmeltblown-grade polyethylene or polypropylene for wet-laid microfiberspinning creates opportunities for cost reduction when used inbath/facial tissue or towel manufacturing, and in increased use ofbio-based renewable material content, all of which are consistent withsustainability objectives.

Many companies wish to reduce their forest fiber footprints. A keycomponent in achieving this goal can be to transfer a significantportion of wood fiber sourced from natural forests to alternative,renewable sources. In certain cases, this goal calls for a reduction innorthern bleached softwood Kraft (NBSK) pulp. Products such as tissue,towels, and industrial wipers are responsible for a significant portionof virgin NBSK consumption. NBSK can be the most expensive fiber among acompany's spend on commodity pulps annually. There are alsouncertainties with respect to long softwood fiber supply andfluctuations in NBSK prices. The initiative described herein, generallyNBSK replacement using a low-cost wet-laid microfiber, is a timelyinitiative to support corporate sustainability. The fibers describedherein can also be used in any other suitable nonwoven process includingthe production of bonded carded webs.

The present disclosure employs a thermoplastic starch. Starch is anatural polymer composed of amylose and amylopectin. Amylose isessentially a linear polymer having a molecular weight in the range of100,000-500,000, whereas amylopectin is a highly branched polymer havinga molecular weight of up to several million. Although starch is producedin many plants, typical sources includes seeds of cereal grains, such ascorn, waxy corn, wheat, sorghum, rice, and waxy rice; tubers, such aspotatoes; roots, such as tapioca (i.e., cassava and manioc), sweetpotato, and arrowroot; and the pith of the sago palm. Broadly speaking,any natural (unmodified) and/or modified starch may be employed in thepresent invention. Modified starches, for instance, are often employedthat have been chemically modified by typical processes known in the art(e.g., esterification, etherification, oxidation, acid hydrolysis,enzymatic hydrolysis, etc.). Starch ethers and/or esters may beparticularly desirable, such as hydroxyalkyl starches, carboxymethylstarches, etc. The hydroxyalkyl group of hydroxylalkyl starches maycontain, for instance, 2 to 10 carbon atoms, in some embodiments from 2to 6 carbon atoms, and in some embodiments, from 2 to 4 carbon atoms.Representative hydroxyalkyl starches such as hydroxyethyl starch,hydroxypropyl starch, hydroxybutyl starch, and derivatives thereof.Starch esters, for instance, may be prepared using a wide variety ofanhydrides (e.g., acetic, propionic, butyric, and so forth), organicacids, acid chlorides, or other esterification reagents. The degree ofesterification may vary as desired, such as from 1 to 3 ester groups perglucosidic unit of the starch.

Regardless of whether it is in a native or modified form, the starch maycontain different percentages of amylose and amylopectin, different sizestarch granules and different polymeric weights for amylose andamylopectin. High amylose starches contain greater than about 50% byweight amylose and low amylose starches contain less than about 50% byweight amylose. Although not required, low amylose starches having anamylose content of from about 10% to about 40% by weight, and in someembodiments, from about 15% to about 35% by weight, are particularlysuitable for use in the present invention. Examples of such low amylosestarches include corn starch and potato starch, both of which have anamylose content of approximately 20% by weight. Such low amylosestarches typically have a number average molecular weight (“Mn”) rangingfrom about 50,000 to about 1,000,000 grams per mole, in some embodimentsfrom about 75,000 to about 800,000 grams per mole, and in someembodiments, from about 100,000 to about 600,000 grams per mole, as wellas a weight average molecular weight (“Mw”) ranging from about 5,000,000to about 25,000,000 grams per mole, in some embodiments from about5,500,000 to about 15,000,000 grams per mole, and in some embodiments,from about 6,000,000 to about 12,000,000 grams per mole. The ratio ofthe weight average molecular weight to the number average molecularweight (“Mw/Mn”), i.e., the “polydispersity index”, is also relativelyhigh. For example, the polydispersity index may range from about 20 toabout 100.

A plasticizer is also employed in the thermoplastic starch to helprender the starch melt-processible. Starches, for instance, normallyexist in the form of granules that have a coating or outer membrane thatencapsulates the more water-soluble amylose and amylopectin chainswithin the interior of the granule. When heated, plasticizers may softenand penetrate the outer membrane and cause the inner starch chains toabsorb water and swell. This swelling will, at some point, cause theouter shell to rupture and result in an irreversible destructurizationof the starch granule. Once destructurized, the starch polymer chainscontaining amylose and amylopectin polymers, which are initiallycompressed within the granules, will stretch out and form a generallydisordered intermingling of polymer chains. Upon resolidification,however, the chains may reorient themselves to form crystalline oramorphous solids having varying strengths depending on the orientationof the starch polymer chains. Because the starch is thus capable ofmelting and resolidifying at certain temperatures, it is generallyconsidered a “thermoplastic starch.”

Suitable plasticizers may include, for instance, polyhydric alcoholplasticizers, such as sugars (e.g., glucose, sucrose, fructose,raffinose, maltodextrose, galactose, xylose, maltose, lactose, mannose,and erythrose), sugar alcohols (e.g., erythritol, xylitol, malitol,mannitol, and sorbitol), polyols (e.g., ethylene glycol, glycerol,propylene glycol, dipropylene glycol, butylene glycol, and hexanetriol), etc. Also suitable are hydrogen bond forming organic compoundswhich do not have hydroxyl group, including urea and urea derivatives;anhydrides of sugar alcohols such as sorbitan; animal proteins such asgelatin; vegetable proteins such as sunflower protein, soybean proteins,cotton seed proteins; and mixtures thereof. Other suitable plasticizersmay include phthalate esters, dimethyl and diethylsuccinate and relatedesters, glycerol triacetate, glycerol mono and diacetates, glycerolmono, di, and tripropionates, butanoates, stearates, lactic acid esters,citric acid esters, adipic acid esters, stearic acid esters, oleic acidesters, and other acid esters. Aliphatic acids may also be used, such ascopolymers of ethylene and acrylic acid, polyethylene grafted withmaleic acid, polybutadiene-co-acrylic acid, polybutadiene-co-maleicacid, polypropylene-co-acrylic acid, polypropylene-co-maleic acid, andother hydrocarbon based acids. A low molecular weight plasticizer ispreferred, such as less than about 20,000 g/mol, preferably less thanabout 5,000 g/mol and more preferably less than about 1,000 g/mol.

The relative amount of starches and plasticizers employed in thethermoplastic starch may vary depending on a variety of factors, such asthe desired molecular weight, the type of starch, the affinity of theplasticizer for the starch, etc. Typically, however, starches constitutefrom about 30 wt. % to about 95 wt. %, in some embodiments from about 40wt. % to about 90 wt. %, and in some embodiments, from about 50 wt. % toabout 85 wt. % of the thermoplastic starch. Likewise, plasticizerstypically constitute from about 5 wt. % to about 55 wt. %, in someembodiments from about 10 wt. % to about 45 wt. %, and in someembodiments, from about 15 wt. % to about 35 wt. % of the thermoplasticcomposition. It should be understood that the weight of starchreferenced herein includes any bound water that naturally occurs in thestarch before mixing it with other components to form the thermoplasticstarch. Starches, for instance, typically have a bound water content ofabout 5% to 16% by weight of the starch.

Additional information with respect to the processing and use ofthermoplastic starch can be found in U.S. Pat. No. 8,470,222 to Shi etal., which is incorporated herein by reference to the extent it does notconflict herewith.

Conventional synthetic microfibers are made in a conventional fiberspinning process (not a meltblown process) from conventional fiber-gradepolymer. The process described herein substitutes a blend of lessexpensive meltblown-grade polyolefin(s) and a low-cost thermoplasticmodified starch (TPMS). These blends can be made with or without acompatibilizer, such as maleic anhydride grafted polymers or polar-groupgrafted polymeric additives or coupling agents. The wet-laid microfiberdescribed herein can be in any cross-sectional configurations such asmonofilament, side-by side, island-in-the sea, or sheath-corestructures. The fibers can be cut into staple fibers or used as acontinuous fiber without cutting. For tissue applications, the fibersare cut into lengths less than 5 mm, with a normal range of 1 mm to 3 mmlong.

If TPMS is added to fiber-grade polyolefins in a conventionalfiber-spinning process, fibers cannot be spun without the fibersbreaking except at very low speeds. Further, TPMS and meltblown-gradepolyolefins are not able to be spun into fiber on their own becausetheir MFIs are either too low (TPMS) or too high (meltblown-gradepolyolefins) to produce fibers.

The microfibers produced herein can be optionally surface treated with asurfactant for use in a wet-laid process. These microfibers, with orwithout surfactant treatment, can be used in tissue/towel substrates,absorbent articles, and in any other suitable application.

The present disclosure relates to microfiber material compositions andmethods for thermoplastic starch extrusion converting, compounding, andwet-laid microfiber fabrication for tissue and towel applications.Examples containing meltblown-grade polyolefin and TPMS can be blendedwith or without any compatibilizer, including but not limited to, maleicanhydride grafted polymers or polar-group grafted polymeric additives orcoupling agents for successful fiber spinning. Experimental dataindicates these blends can be spun into a fiber, which is then surfacetreated using a selected surfactant to create a wet-laid fiber forpapermaking.

To be hydrophilic or wettable for tissue or towel applications, themicrofiber surface can be treated by surfactants such as SF-19 duringmicrofiber spinning or a surfactant could be compounded into the fiberblends outlined in U.S. Pat. No. 5,759,926 to Pike et al.

EXAMPLES

The following is provided for exemplary purposes to facilitateunderstanding of the disclosure and should not be construed to limit thedisclosure to the examples. Other formulations and substrates can beused within this disclosure and the claims presented below.

Materials

Hydroxypropylated corn starch, GLUCOSOL 800, was purchased from Chemstar(Minneapolis, Minn.) with a weight-averaged molecular weight, determinedby GPC, of 2,900,000 and a polydispersity estimated at 28. The modifiedstarch has a bulk density of 0.64 g/cm³, its particle sizes pass 98% minthrough 140 Mesh, and it is supplied as off-white powders.

METOCENE MF650X metallocene polypropylene homopolymer, purchased fromLyondellbasell (Carrollton, Tex.), has a specific density of 0.91 g/cm³and a melt flow index (230° C./2.16 kg) of 1200 g/10 min.

DNDA-1082 linear low density polyethylene, purchased from the DowChemical Company (Midland, Mich.), has a specific density is 0.94 g/cm³and a melt flow index (190° C./2.16 kg) of 160 g/10 min.

PPH 3762 polypropylene homopolymer and PPH M3766 metallocene isostaticpolypropylene were purchased from Total Petrochemicals (Houston, Tex.).The specific density and melt flow index for PPH 3762 are 0.91 g/cm³ and18 g/10 min (190° C./2.16 kg) and those for PPH M3766 are 0.90 g/cm³ and23 g/10 min (190° C./2.16 kg).

PLA 6201 D fiber-grade polylactic acid was purchased from NatureWorks(Minnetonka, Minn.), with a specific density of 1.24 g/cm³ and a meltflow index (190° C./2.16 kg) of 15 to 30 g/10 min.

FUSABOND E528 anhydride-modified polyethylene and FUSABOND 353chemically-modified polypropylene copolymer are used as compatibilizers,purchased from DuPont (Wilmington, Del.).

INFUSE 9807 high-performance olefin block copolymer is purchased fromthe Dow Chemical Company (Midland, Mich.). It has a density of 0.87g/cm³ and a melt flow index of 15 g/10 min (190° C. and 2.16 kg).

Masil SF-19 is a surfactant used to make a fiber surface hydrophilic. Itwas purchased from Lubrizol Inc. (Spartanburg, S.C.).

Material Processing

Example 1: Making Thermoplastic Modified Starch (TPMS) Using GLUCOSOL800 Biopolymer

A K-TRON feeder (K-Tron America, Pitman, N.J.) was used to feed thestarch material into a ZSK-30 extruder (Werner and PfleidereCorporation, Ramsey, N.J.). The ZSK-30 extruder is a co-rotating, twinscrew extruder. The extruder diameter is 30 mm with the length of thescrews up to 1328 mm. The extruder has 14 barrels, numberedconsecutively 1-14 from the feed hopper to the die. The first barrel(#1) received the modified starch at 15 lbs./hr. when the extruder washeated to the temperature profile as shown in Table 1 and the screw wasset to rotate at 170 rpm. Glycerin as a plasticizer was pumped intobarrel #2 using an Eldex pump from Eldex Laboratories, Inc. (Napa,Calif.). The vent was opened at the end of the extruder to releasemoisture. The die used to convert starch to thermoplastic starch has 3openings of 5 mm in diameter that were separated by 3 mm. Thethermoplastic starch strands were cooled on a conveyer belt and thenpelletized.

TABLE 1 Processing Conditions for Making TPMS on ZSK-30 Material FeedingExtruder Sample Rate Modified Glycerin Speed Extruder TemperatureProfile (° C.) P_(melt) Torque No. (lb/hr) Starch (%) (rpm) T₁ T₂ T₃ T₄T₅ T₆ T₇ T_(melt) (psi) (%) Example 1 15 75 25 170 80 105 137 150 145142 140 155 60-70 50-60

The following examples were made similarly to those of Example 1 withthe exception that no glycerin was needed. All processing conditionssuch as temperatures, screw speed, etc. from Example 2 to Example 10 arelisted in Table 2 below.

TABLE 2 Processing Conditions for Compounding TPMS with Polyolef ins onZSK-30 Resin Non- Feeding DNDA MF650X Meltblown Extruder Rate TPMS 1082PE PP PPH Speed Extruder Temperature Profile (° C.) P_(melt) TorqueSample No. (lb/hr) (%) (%) (%) (%) (rpm) T₁ T₂ T₃ T₄ T₅ T₆ T₇ T_(melt)(psi) (%) Example 2 20 10 90* 160 99 118 141 155 161 145 144 167 20-2546-51 Example 3 20 20 80* 160 99 118 141 155 161 145 144 167 20-25 63-68Example 4 20 30 70* 160 99 118 141 155 161 145 144 167 20-25 61-70Example 5 20 25 75* 160 100 121 140 155 160 145 145 164 20-25 58-64Example 6 20 10 90  160 100 120 140 155 160 147 145 162 10-20 61-66Example 7 20 20 80  160 100 120 140 155 160 147 145 162 18-20 71-78Example 8 20 30 70** 160 100 120 140 155 160 147 145 162 18-22 60-65Example 9 20 Example 8 @ 50% 50* 160 100 120 140 155 160 147 145 16220-23 40-43 Example 10 20 10 (M3766) 90* 160 140 150 160 160 160 160 164191 120-125 64-66 *FUSABOND 353 chemically-modified polypropylenecopolymer used at about 1%. **FUSABOND E528 anhydride-modifiedpolyethylene used at about 1%.

Examples 2 to 5 were blends created using TPMS made from Example 1 andmeltblown-grade polypropylene with a compatibilizer.

Examples 6 to 7 were blends created using TPMS made from Example 1 andmeltblown-grade polypropylene without any compatibilizer.

Example 8 was a blend created using TPMS made from Example 1 andmeltblown-grade polyethylene with a compatibilizer.

Example 9 was a blend created by compounding Example 8 and themeltblown-grade PP using 5% INFUSE 9807 high-performance olefin blockcopolymer as a compatibilizer for polyolefin resins.

Examples 10 is a blend created using non-meltblown-grade polypropylene(PPH M3766) and TPMS with a compatibilizer.

Thermal Properties

The melt flow rate (MFR) is the weight of a polymer (in grams) forcedthrough an extrusion rheometer orifice (0.0825-inch diameter) whensubjected to a load of 2160 grams in 10 minutes, typically at 190° C. or230° C. Unless otherwise indicated, the melt flow rate was measured inaccordance with ASTM Test Method D1239 with a melt indexer (TiniusOlsen, Willow Grove, Pa.). The melt flow indexes for all 10 exampleswere measured and are listed in Table 3. The melt flow index value forTPMS is close to be negligible. In comparison to the neatmeltblown-grade polypropylene, the melt flow index values for the blendscontaining TPMS are significantly lower. Example 8 is the blend usingmeltblown-grade polyethylene and TPMS (70/30); its melt flow index valueis also significantly lower relative to the neat meltblown-gradepolyethylene.

TABLE 3 Fiber Blend Melt Flow Index (in g/10 min) Example 1 2 3 4 5 6 78 9 10 MFI <0.5 646 499 375 412 609 478 60 200 13

A Differential Scanning calorimeter (DSC) analysis was carried out tounderstand the thermal properties of the resin samples. Pellet sampleswere analyzed using a TA Instruments Q200 Differential Scanningcalorimeter. A DSC thermogram for a sample (approximately 5 mg) in asealed aluminum pan was recorded in the temperature range of 50° C. to200 QC under a dynamic nitrogen atmosphere using a heating/cooling rateof 10° C./min. Universal analysis NT software provided by TA Instrumentswas used for analyzing data.

DSC thermograms (2nd heat) for blends of PP with TPMS amounts rangingfrom 10% to 20% to 30% (resin samples made from Examples 2, 3, and 4)are compared in FIG. 1. As shown in FIG. 2, the melting temperatures forall blends are around 154° C., which is the melting temperature of neatmeltblown-grade polypropylene. The results show that the melttemperature does not vary significantly with increasing TPMS content.The melt enthalpy, however, which is displayed in FIG. 3, decreased from99 J/g (the neat meltblown-grade polypropylene) to about 75 J/g for thePP/TPMS (70/30) blend, indicating a decrease in crystallinity.

Fiber Spinning

A fiber spinning line (Davis Standard Corporation, Pawcatuck, Conn.),which consists of two extruders, a quench chamber, and a godet with amaximal speed of 3000 meters per minute was used for melt fiberspinning. The spinning line had the capacity to make monofilament,side-by-side, and sheath core fibers. The spinning die plate used forthe monofilament fiber samples presented in this disclosure was a16-hole plate with each hole having a diameter of 0.4 mm. Only oneextruder was used. Table 4 outlines the fiber spinning processingconditions and corresponding sample codes.

TABLE 4 Fiber Spinning Parameters Extruders for Sample 11 Sample No.Examples 2 to 4 Examples 6 to 7 Example 10 Sheath Core Extruder Zone 7(° C.) 175 160 210 200 180 Zone 6 (° C.) 175 160 210 200 180 Zone 5 (°C.) 165 160 174 200 180 Zone 4 (° C.) 170 160 210 200 180 Zone 3 (° C.)170 150 210 195 180 Zone 2 (° C.) 170 150 200 195 175 Zone 1 (° C.) 153140 165 195 175 Ext 1 Melt 90 65 1145 650 790 Outlet Pressure (psi)Spinning Spin Beam 180 160 190 195 Temp and (° C.) Speed Godet Speed700, 500, 300 700, 500, 300 300 700, 500, 300 (m/min) Misc. Ext 1 Melt6.6 9 14.6 2 18 Pump (rpm) Pack Type Monofilament MonofilamentMonofilament Sheath/Core

Example 11 was a sheath core fiber, where the core material was fromExample 9 and the sheath material is PLA 6201 D fiber-grade polylacticacid at a ratio of (90/10).

Fiber Properties

Individual fiber specimens were shortened (i.e., cut with scissors) to38 mm in length and placed separately on a black velvet cloth. 10 to 15fiber specimens were collected in this manner. The fiber specimens werethen mounted in a substantially straight condition on a rectangularpaper frame having external dimensions of 51 mm×51 mm and internaldimensions of 25 mm×25 mm. The ends of each fiber specimen wereoperatively attached to the frame by carefully securing the fiber endsto the sides of the frame with adhesive tape. Each fiber specimen wasthen measured for its external, cross-fiber dimension employing aconventional laboratory microscope that was properly calibrated and setat 40× magnification. This cross-fiber dimension was recorded as thediameter of the individual fiber specimen. The frame helped to mount theends of the sample fiber specimens in the upper and lower grips of aconstant rate of extension type tensile tester, MTS SYNERGY 200 tensiletester from MTS Systems Corporation (Eden Prairie, Mich.).

Tenacity values were expressed in terms of gram-force per denier. Thedenier is the mass in grams per 9000 meters of fiber. Peak elongation (%strain at break), peak stress, and peak load were also measured.

Fiber mechanical properties were determined for the blends at 300 and500 meters per minute drawing speeds. The properties of fibers spun at700 m/min were not tested. The results are tabulated in Table 5.

TABLE 5 Fiber Mechanical Properties Fiber Drawing Peak Peak Speed LoadStress Elongation Denier Example No. Blend Ratio (m/min) (gf) (MPa) (%)Tenacity (gf) Example 2 PP/TPMS (90/10) 300 3.6 30.7 132 0.37 9.3 5002.5 37.0 277 0.47 5.4 Example 3 PP/TPMS (80/20) 300 3.8 33.4 693 0.428.9 500 2.5 39.6 655 0.50 5.2 Example 4 PP/TPMS (70/30) 300 3.4 27.1 5810.34 10.2 500 2.0 41.6 472 0.52 3.9 Example 6 PP/TPMS (90/10) 300 2.027.6 188 0.35 6.0 500 2.1 44.1 235 0.56 4.0 Example 7 PP/TPMS (80/20)300 1.9 27.2 164 0.34 6.9 500 1.8 35.8 199 0.46 5.1 Example 10PP3766/TPMS (90/10) 300 11.9 102 667 1.28 9.3 500 N/A N/A N/A N/A N/AExample 12 PLA/Example 9 (10/90) 300 8.7 37.5 233 0.47 21.3 500 5.4 48.8197 0.61 9.9

As indicated, fiber elongation improved with an increasing amount of themodified thermoplastic starch in Examples 3 and 4 relative to Example 2.The blends containing no FUSABOND compatibilizer shown in Examples 6 and7 can be spun into fibers but fiber elongation is relatively low.Example 10 can be spun into fiber only at 300 m/min; at 500 m/min thefiber could not be spun for tenacity testing. The fiber diameters variedbut were mostly about 30 to 40 microns, depending on fiber drawingspeed. The fiber peak stress improved as fiber drawing speed isincreased.

Meltblown-grade polyolefins are commonly used to make meltblown webs fornonwoven applications. The prior art does not teach how to compoundmeltblown-grade polyolefin with thermoplastic modified starch forshort-cut wet-laid microfibers in tissue or towel applications. Fiberswere surprisingly able to be spun from the novel blends describedherein. These new wet-laid microfiber compositions and fabricationprocesses produced results not previously thought possible.

In a first particular aspect, spun microfibers include a blend of 70 wt.% to 90 wt. % meltblown-grade polyolefin and 10 wt. % to 30 wt. %thermoplastic starch, wherein the microfibers are suitable for use in awet-laid process.

A second particular aspect includes the first particular aspect, whereinthe blend prior to spinning has a melt flow index greater than 150.

A third particular aspect includes the first and/or second aspect,wherein the microfibers are staple fibers.

A fourth particular aspect includes one or more of aspects 1-3, furtherincluding a surfactant treatment.

A fifth particular aspect includes one or more of aspects 1-4, the blendfurther including a compatibilizer.

A sixth particular aspect includes one or more of aspects 1-5, whereinthe meltblown-grade polyolefin is polypropylene.

A seventh particular aspect includes one or more of aspects 1-6, whereinthe meltblown-grade polyolefin is polyethylene.

An eighth particular aspect includes one or more of aspects 1-7, whereinthe starch is a native starch derived from cereal grains such as corn,waxy corn, wheat, sorghum, rice, and waxy rice; tubers such as potatoes;roots such as tapioca, sweet potato, and arrowroot; or the pith of thesago palm.

A ninth particular aspect includes one or more of aspects 1-8, whereinnative starch has been modified to become thermoplastic modified starch(TPMS).

In a tenth aspect, a method for producing spun microfibers includesproducing a blend of 70 wt. %-90 wt. % meltblown-grade polyolefin with10 wt. % to 30 wt. % thermoplastic modified starch (TPMS) derived fromnative starch; and spinning the blend into microfibers in a fiberspinning process, wherein the microfibers are suitable for use in awet-laid process.

An eleventh particular aspect includes the tenth particular aspect,wherein the blend prior to spinning has a melt flow index greater than150.

A twelfth particular aspect includes the eleventh and/or tenth aspect,further including cutting the microfibers into staple fibers.

A thirteenth particular aspect includes one or more of aspects 10-12,further including applying a surfactant treatment to the microfibers.

A fourteenth particular aspect includes one or more of aspects 10-13,wherein the blend further includes a compatibilizer.

A fifteenth particular aspect includes one or more of aspects 10-14,wherein the meltblown-grade polyolefin is polypropylene.

A sixteenth particular aspect includes one or more of aspects 10-15,wherein the meltblown-grade polyolefin is polyethylene.

A seventeenth particular aspect includes one or more of aspects 10-16,wherein the native starch is derived from cereal grains such as corn,waxy corn, wheat, sorghum, rice, and waxy rice; tubers such as potatoes;roots such as tapioca, sweet potato, and arrowroot; or the pith of thesago palm.

In an eighteenth particular aspect, a method for producing an absorbentproduct includes producing a blend of 70 wt. %-90 wt. % meltblown-gradepolyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch(TPMS), wherein the blend prior to spinning has a melt flow indexgreater than 150; spinning the blend into microfibers in a fiberspinning process; cutting the microfibers into staple fibers; andincorporating the staple fibers into a wet-laid process for making anonwoven web.

A nineteenth particular aspect includes the eighteenth particularaspect, further including converting the nonwoven web into an absorbentproduct.

A twentieth particular aspect includes the eighteenth and/or nineteenthaspects, wherein the absorbent product is a tissue product.

In the interests of brevity and conciseness, any ranges of values setforth in this disclosure contemplate all values within the range and areto be construed as support for claims reciting any sub-ranges havingendpoints that are whole number values within the specified range inquestion. By way of hypothetical example, a disclosure of a range offrom 1 to 5 shall be considered to support claims to any of thefollowing ranges: 1 to 5; 1 to 4; 1 to 3; 1 to 2; 2 to 5; 2 to 4; 2 to3; 3 to 5; 3 to 4; and 4 to 5.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

All documents cited in the Detailed Description are, in relevant part,incorporated herein by reference; the citation of any document is not tobe construed as an admission that it is prior art with respect to thepresent disclosure. To the extent that any meaning or definition of aterm in this written document conflicts with any meaning or definitionof the term in a document incorporated by references, the meaning ordefinition assigned to the term in this written document shall govern.

While particular aspects of the present disclosure have been illustratedand described, it would be obvious to those skilled in the art thatvarious other changes and modifications can be made without departingfrom the spirit and scope of the disclosure. It is therefore intended tocover in the appended claims all such changes and modifications that arewithin the scope of this disclosure.

We claim:
 1. Spun microfibers comprising a blend of 70 wt. % to 90 wt. %meltblown-grade polyolefin and 10 wt. % to 30 wt. % thermoplasticstarch, wherein the microfibers are suitable for use in a wet-laidprocess.
 2. The spun microfibers of claim 1, wherein the blend prior tospinning has a melt flow index greater than
 150. 3. The spun microfibersof claim 1, wherein the microfibers are staple fibers.
 4. The spunmicrofibers of claim 1, further comprising a surfactant treatment. 5.The spun microfibers of claim 1, the blend further comprising acompatibilizer.
 6. The spun microfibers of claim 1, wherein themeltblown-grade polyolefin is polypropylene.
 7. The spun microfibers ofclaim 1, wherein the meltblown-grade polyolefin is polyethylene.
 8. Thespun microfibers of claim 1, wherein the starch is a native starchderived from cereal grains such as corn, waxy corn, wheat, sorghum,rice, and waxy rice; tubers such as potatoes; roots such as tapioca,sweet potato, and arrowroot; or the pith of the sago palm.
 9. The spunmicrofibers of claim 8, wherein native starch has been modified tobecome thermoplastic modified starch (TPMS).
 10. A method for producingspun microfibers comprising: producing a blend of 70 wt. %-90 wt. %meltblown-grade polyolefin with 10 wt. % to 30 wt. % thermoplasticmodified starch (TPMS) derived from native starch; and spinning theblend into microfibers in a fiber spinning process, wherein themicrofibers are suitable for use in a wet-laid process.
 11. The methodof claim 10, wherein the blend prior to spinning has a melt flow indexgreater than
 150. 12. The method of claim 10, further comprising cuttingthe microfibers into staple fibers.
 13. The method of claim 10, furthercomprising applying a surfactant treatment to the microfibers.
 14. Themethod of claim 10, wherein the blend further comprises acompatibilizer.
 15. The method of claim 10, wherein the meltblown-gradepolyolefin is polypropylene.
 16. The method of claim 10, wherein themeltblown-grade polyolefin is polyethylene.
 17. The method of claim 10,wherein the native starch is derived from cereal grains such as corn,waxy corn, wheat, sorghum, rice, and waxy rice; tubers such as potatoes;roots such as tapioca, sweet potato, and arrowroot; or the pith of thesago palm.
 18. A method for producing an absorbent product, the methodcomprising: producing a blend of 70 wt. %-90 wt. % meltblown-gradepolyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch(TPMS), wherein the blend prior to spinning has a melt flow indexgreater than 150; spinning the blend into microfibers in a fiberspinning process; cutting the microfibers into staple fibers; andincorporating the staple fibers into a wet-laid process for making anonwoven web.
 19. The method of claim 18, further comprising convertingthe nonwoven web into an absorbent product.
 20. The method of claim 18,wherein the absorbent product is a tissue product.